CHICAGO (Reuters) - Some 56 percent of U.S. consumers think Wal-Mart Stores Inc. is bad for America, according to a Zogby International poll released on Thursday by one of the retailer's most vocal critics.

The national poll -- commissioned by WakeUpWalMart.com, a union-funded group that has been pressuring Wal-Mart to raise employee wages and benefits -- surveyed 1,012 randomly chosen adults on their attitudes toward the world biggest retailer.

Respondents were asked to choose which of two statements more closely fit their personal opinions.

The majority, or 56 percent, picked: "I believe that Wal-Mart is bad for America. It may provide low prices, but these prices come with a high moral and economic cost for consumers." Thirty-nine percent agreed that "Wal-Mart is good for America. It provides low prices and saves consumers money every day."

Wal-Mart questioned the timing of the poll, which was conducted from November 15 to 18 -- a week when many of the retailer's critics organized events to highlight their concerns about the company, and screened a widely publicized documentary that cast Wal-Mart in a negative light.

"This poll is another way for them (WakeUpWalMart) to reach out for something to try to validate their efforts because they don't have anything else to hang their hat on," Wal-Mart spokeswoman Sarah Clark said.

The poll was released on the same day that Wal-Mart reported a 4.3 percent increase in November sales at its U.S. stores open at least a year -- a key retail measure known as same-store sales. Wal-Mart has about 3,700 U.S. stores and 2,400 international locations, and is expected to generate more than $300 billion in revenues in the current fiscal year.

Wal-Mart, the largest U.S. private-sector employer, faces intense pressure at home from unions, environmental groups and others who say the company pays poverty-level wages, offers poor health-care benefits and gobbles up green space with its massive big-box stores.

At the same time, Wal-Mart is defending a record-large class-action lawsuit that charges it with discriminating against women in pay and promotions.

Wal-Mart denies those claims, and points out that it often receives thousands of applications for a few hundred jobs when it opens new stores.

Wal-Mart, which hired a team of public relations experts to help polish its image, said critics' efforts to discredit the company have had little success, judging from the more than 100 million U.S. customers who shop its stores every week.

But WakeUpWalMart lauded the poll as evidence that consumers are increasingly aware of the concerns the group has worked to spotlight.

"Despite two high-priced image make-overs, Wal-Mart's public image is in a tailspin," Paul Blank, campaign director for WakeUpWalMart, said in a statement.

The Zogby poll also questioned consumers on whether they thought that Wal-Mart was becoming too powerful an economic force in America. Some 33 percent were very concerned, while 20 percent said they were not at all concerned.

Thirty-three percent strongly agreed that Wal-Mart was a retail monopoly that threatened the future health of the U.S. economy, but 35 percent did not agree at all.